Hot melt mix applicators are used to apply hot melt mix, in the form of an asphalt or bituminous hot melt material, on areas such as paved roads and the like for sealing, patching, or repairing the roads. These types of applicators are also used to apply hot melt material to hold in place raised or recessed pavement markers and to seal and protect inductive traffic loops.
In one such commercially successful hot melt mix applicator heretofore marketed by the assignee herein and disclosed in U.S. Pat. No. 4,692,028, the applicator has a tank for heating and storing hot melt mix that is pumped by a pump through a hose and a wand onto pavement. During periods of operation where an operator wishes not to apply mix, but desires the mix to remain hot enough to be applied on demand, the wand is inserted into a holster connected to the tank. With the wand in the holster, the pump continuously circulates mix through the hose, wand, holster and back into the tank so that it will not harden in the wand or hose and obstruct flow.
When use of the applicator is finished, the pump is briefly reversed to clear the hose and wand of hot melt mix material before the hot melt mix is allowed to cool. Unfortunately, should hot melt mix harden within either the hose or the wand, it can partially obstruct or completely block flow through the hose causing an operator to have to clean out the hose and wand before the applicator can be used to apply hot melt mix.
To improve upon this method of preventing obstruction of the hose and wand, a single phase electrical heating system has been used to prevent hot mix material from solidifying in the hose and wand. In operation, a temperature sensor on the wand or hose communicates temperature to a controller which regulates the heat input of a heating element of the system that is in contact with the hose and wand by regulating electric power applied to the element.
In the construction of the heating element, a single heating element wire and a non-heating neutral wire makeup a two-wire heating element cord that is wrapped around the hose and wand in a spiral or helical fashion. Unfortunately, a rather dangerous electric potential of at least about 110 volts A.C. is applied to the heating element during operation to heat the hose and wand. As a result, the risk of shock is great should wires become exposed or otherwise become insufficiently insulated during operation.
Additionally, because only one wire of the pair of wires of the heating element cord wrapped around the hose can generate and transmit heat, the cord must be relatively tightly coiled around the hose and wand with a minimum of space between coils to provide the proper heat flux to prevent the hot melt mix from solidifying. Unfortunately, since only one wire of the two wire heating element cord can generate heat and since both wires of the cord bear against the hose and wand, the amount of heating element wire per unit length of cord is not maximized leading to less efficient heating element operation.
Moreover, for particularly long lengths of hose, such as hoses that are about twelve feet in length or longer, more than one temperature sensor must be used in a single phase heating system to provide adequate temperature regulation so that the hose and wand will be properly heated during operation. This additional sensor disadvantageously increases the cost and potential maintenance of the heating system while it also increases the complexity and difficulty of properly heating both the wand and hose to maintain them at a temperature which will ensure good hot melt mix flow through the hose and wand.
In the control of the heating element, the temperature controller simply regulates current flow from a single phase alternator to the heating element by turning current flow on and off. In determining whether current flow should be supplied, the controller has a selectively adjustable thermostat which communicates with the temperature sensor. If the sensed temperature is too high, the thermostat will cause the controller to turn off current flow to the heating element. If the sensed temperature is too low, the thermostat will cause the controller to turn on current flow to the heating element.
To control single phase current flow, the controller is wired in series with the heating element and simply functions as an on/off switch in response to input from a temperature sensor in communication with the hose or wand. The controller does not control operation of the alternator nor the engine. It simply functions as a switch to turn on and off current flow to the heating element.
The alternator is a conventional alternator that is connected by pulleys and a belt to a drive shaft of an internal combustion engine for supplying electrical power. The alternator has an integral power regulation circuitry to convert its raw three phase lower voltage output into single phase A.C. current having a regulated voltages of at least about 110 volts. Unfortunately, this power regulation circuitry adds to the cost of the system without adding any advantage in its use or operation.
What is needed is a more efficient and economical wand and hose heating system that more safely operates at lower voltages while still providing adequate heat to maintain hot melt mix within the hose and wand at a flowable state. What is also needed is a hot melt mix applicator of relatively compact and mobile construction that has a heated hose and wand for maximizing convenience and performance of the applicator.